ABSTRACT
The interactive relationship between soil and water is fundamental to plant growth and many other ecosystem services provided by soils, from hosting large microbial biodiversity to providing habitat to soil fauna and from filtering water to regulating trace gas emissions. These interactions are complex and dynamic, relying on the capacity of soils to retain and filter water as well as transport and transform nutrients and other chemicals. Soil health, as defined by Doran et al. (1996), is ‘the capacity of a living soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and promote plant and animal health’. This indicates that the definition of soil health must go beyond the traditional view of soil as a medium for crop growth alone. In sustainable agriculture, soils must not only provide sufficient water for crop growth, but also prevent rapid transport of fertilizers, pesticides and sediment to water sources and reduce the potential for soil loss and degradation. These require a balance of storage and fluxes in soils to allow for necessary soil functions, including maintaining an appropriate balance between water-filled and air-filled pore spaces for plant and microbial health, adequate infiltration to prevent surface ponding and runoff, and suitable drainage to prevent saturated subsurface conditions. Integral to all of these soil functions is the storage and movement of water in soils.
